The present invention relates to a pain sensory nerve stimulation apparatus which can adequately perform selective stimulation of desired nerve fibers (particularly, C fibers) of a living body.
As described in JP-A-2010-088802, in order to early detect a disorder of peripheral nerve which is one of the three major complications of diabetes, a method in which only C fibers are stimulated and a reaction to the stimulation is checked is highly requested.
JP-A-2010-088802 discloses a pain sensory nerve stimulation apparatus which can stimulate only C fibers. In the proposed apparatus, only C fibers can be selectively stimulated, and various applications are expected. Also in the case where stimulation is performed by the pain sensory nerve stimulation apparatus, however, there are individual variations, and, even for healthy individuals, different reactions to the same stimulation intensity (mA) sometimes occur.
JP-A-2010-088802 discloses that, when the stimulation intensity based on the current amount is low, C fibers are stimulated, and, as the stimulation intensity becomes higher, thicker fibers such as Aδ fibers are stimulated. However, there are individual variations in sensitivity to stimulation. When the stimulation intensity is increased, therefore, desired fibers cannot be stimulated. Moreover, a stimulation intensity based on a large current amount causes the subject to feel pain. Therefore, a stimulation technique may be possible in which, in the initial stage of measurement, stimulation is started at an intensity based on a small current amount, and then gradually changed to have an intensity based on a large current amount.
According to the stimulation technique, however, the reaction becomes duller as time progresses, or the reaction becomes hypersensitive with the elapse of time, thereby causing a problem in that an adequate result cannot be obtained. In the case where only C fibers are to be selectively stimulated as disclosed in JP-A-2010-088802 discloses, particularly, stimulation must be performed by using a very weak current, and, depending on the skill of the inspector, the stimulation may not be adequately performed, so that the inspection sometimes fails to be done well.
U.S. Pat. No. 7,781,486 discloses a technique in which, in order to intensify the action of stimulation using a needle electrode, a substance inhibiting the enzymatic decomposition of endogenous opioide is administered in the form of an intravenous infusion. In the technique, an intravenous infusion is required. Therefore, the technique has a drawback that the technique cannot be simply used for applying stimulus.